This invention relates generally to an imaging apparatus, and more particularly, to a diagnostic imaging apparatus having a rotating portion and a stationary portion with a slip ring between the rotation portion and the stationary portion across which data is transmitted.
In some computed tomography (CT) imaging systems, an x-ray source projects a fan-shaped beam that is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as an “imaging plane.” The x-ray beam passes through an object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of an x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a “view.” A “scan” of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector.
In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts the attenuation measurements from a scan into integers called “CT numbers” or “Hounsfield units,” which are used to control the brightness of a corresponding pixel on a cathode ray tube display or film.
To reduce the total scan time, a “helical” scan may be performed. To perform a “helical” scan, the patient is moved while the data for the prescribed number of slices is acquired. The helix mapped out by the fan beam yields projection data from which images in each prescribed slice may be reconstructed.
Reconstruction algorithms for helical scanning typically use helical weighing algorithms that weight the collected data as a function of view angle and detector channel index. Specifically, prior to a filtered back projection process, the data is weighted according to a helical weighing factor, which is a function of both the gantry angle and detector angle. The helical weighting algorithms also scale the data according to a scaling factor, which is a function of the distance between the x-ray source and the reconstruction plane. The weighted and scaled data is then processed to generate CT numbers and to construct an image that corresponds to a two dimensional slice taken through the object. Alternatively, interpolation can be performed on the collected projection data to produce a set of projections corresponding to the reconstruction plane. Filtered backprojection is then used to construct an image that corresponds to a two-dimensional slice taken through the object.
At least one known CT imaging system during normal scanning sends imaging data collected by a detector array across a slip ring having a shoe and a copper ring mechanism. A receiver of the imaging data checks the data and, if the data is correct, sends an acknowledgement to a transmitter that the correct imaging data was received. However, as scan speeds are increased and additional data is collected in the detector array, data must be transmitted over the slip ring at a faster rate. As a result, there may be insufficient bandwidth to provide a communication path back from the receiver of the imaging data to the transmitter or even to transmit the data itself across the slip ring. Thus, scanning speed is limited by the bandwidth of data transmission across the slip ring.